Compressor case, note the size;The bigger size hole is for male drive rotor.The smaller size on the left is the female rotor, driven.

The end plate, note the wear on the surface on the bigger rotor.Cause by some foreign metal particles.

Gear case housing

Driven rotor, that is the female rotor.

Drive rotor, this case is the male rotor.The gear on the floor is mounted in the gear box to the drive shaft of the main motor, this gear will drive the smaller size gear install on one end of the male rotor shaft.